turbo porting

I ported the turbine wastegate on my diesel turbo a while back and picked up a good increase in midrange power, my question is why? Is it because of lower pumping losses that goes with lower exhaust backpressure or because I have increased the airflow through the engine? Theoretically the turbo should have made less boost with a lower pressure in the exhaust, and therefore less power! Any thoughts?

This is an internal wastegate, the diameter of the exit hole is on the small side, so I enlarged it to just under the size of the penny, and rounded off the sharp edges inside the turbine at the wastegate outlet, I'm thinking that the factory turbine housing is too restrictive for best performance/flow!

More flow for sure....I'm thinking that less back pressure in the exhaust system saps less power from the engine. I think that the velocity of the exhaust gas is the answer here. As engine speed rises so does the velocity of the exhaust gas, so we can still get the same boost from less exhaust manifold pressure by using the kinetic energy of the fast moving gas, and venting any excess pressure via a suitably sized wastegate! I think that this is the reason for building a 4 into 1 exhaust manifold rather than using the log manifolds often found on O.M. engines.